Control system for electric motors



Jan. 5, 1954 FELL CONTROL SYSTEM FOR ELECTRIC MOTORS 2 Sheets-Sheet 1 Filed July 19, 1951 Zl j am 45E 5?. A E a. frumwwl w aujfiw 8 .B wm wmmu REEL. MOTOR FIELD VOLTAGE.

Jan. 5, 1954 E. PELL 2,665,401

CONTROL SYSTEM FOR ELECTRIC MOTORS Filed July 19, 1951 2 Sheets-Sheet 2 C'Dwa. \0

I I5 I x! 'l I :l4 l6 Fl /g Q a 7 J i ll r4 L En' Patented Jan. 5, 1954 2,665,401 CONTROL SYSTEM FOR ELECTRIC MOTORS Eric Pell, Shorewood, Wis.,

Hammer, Inc., of Delaware assignor to Cutler- Milwaukee, Wis., a corporation Application July 19, 1951, Serial No. 237,544

8 Claims. 1

This invention relates to a control system for electric motors, and more particularly to a stalled tension control system for reeling motors.

The processing of long strips of sheet metal usually entails coiling up of the strip on a reel driven by an electric motor. Such reel motors are commonly regulated to constant current by a regulator which regulates the strength of the reel motor field to increase the field strength as the reel diameter increases, and vice versa, to thus provide constant motor C. E. M. F. and constant horsepower for a given linear speed of the strip. However, at or near zero speed of the reel motor its 0. E. M. F. reverts to zero regardless of field strength, and in such speed region it is necessary to provide some other means of regulating the reel motor current to insure maintenance of stalled tension on the strip. One common way of achieving control of the motor current in this speed region is to employ a reel generator having two fields, one of which is energized in proportion to the speed of the mill driving motor,

and the other of which, deemed an auxiliary field, is controlled by the reel motor current regulator in connection with the reel motor field. Another common system employee a reel generator with a single field and a booster in series with the armature of this generator having a field controlled by the reel motor current regulator.

It is a primary object of the present invention to provide improved control systems affording constant current re ulation of a reel motor in the zero speed region employing the reel motor current regulator to regulate, in conjunction with generator having a single field, thereby eliminating the need for a two field reel generator and/or a series booster.

Another object is to provide systems of the aforementioned character wherein the single field of the reel generator is excited proportionately to the speed of the mill motor and the output of the reel motor current regulator, and

A still further object is to provide improved regulator response through employment of a reel generator having a single field winding.

Other objects and advantages of th invention will hereinafter appear.

The accompanying drawings illustrate certain preferred embodiments of the invention which will now be described, it being understood that the embodiments illustrated are susceptible of various modifications in respect of details without departing from the scope of the appended claims.

the reel motor field, the field strength of a reel 2 In the drawings, Figure 1 is a diagrammatic showing of a reeling mechanism together with a control system therefor;

Fig. 2 is a graph depicting certain operating relationship in the system of Fig. 1, and

Fig. 3 is a diagrammatic showing of a reeling mechanism together with a modified form of control system therefor.

Referring to Fig. 1, it shows a length of material lll, such as a strip of steel, passing through mill work rolls H and i2 in the direction of the arrow and being coiled up on a wind-up reel I3.

The mill work rolls l I and I2 are driven by a direct current motor 14 having a separately excited field winding M Field winding M is connected across opposite sides of a source of constant direct current voltage I5 in series with a rheostat [6. Power is supplied to the armature of motor M by an adjustable voltage generator l7, the armature of which is connected in a closed loop with the armature of motor l4. Generator I! is provided with a separately excited field winding I 1 which is connected at one end to one side of source l5 and at its other end to an adjusting element of a potentiometer rheostat H! which has its resistance element connected across opposite sides of source l5. Generator I! may be assumed to be driven at substantially constant speed by any suitable driving means (not shown).

The wind-up reel I3 is driven by a direct current motor [9 having a separately excited field winding [9 Field winding [9 is connected across the source l5 in series with a resistor 20. Power is supplied to the armature of motor i 9 by an adjustable voltage generator 21, the armature of which is connected in a closed loop with the armature of motor IS in series with a resistor 22. Generator 2| is provided with a separately excited field winding 2|, which at one end is connected to one terminal of a tachometer generator 23 in series with resistors 24 and 25, and at its other end is directly connected to the other terminal of tachometer generator 23. Tachomteter 4generator 23 is driven by the shaft of moor I 25 is connected to the adjusting element of a potentiometer rheostat 25 which has its resistfor motor l9 and according to its output acts to vary the excitation of field winding I9 of the motor by counteracting the excitation afforded by the supply source 55. When the output of exciter Z1 is high, its bucking action is correspondingly high and as a result the excitation of field winding w of motor I9 is low. The bucking action of exciter ii-3 reaches a maximum value, which because of blocking rectifier 28 cannot beexceeded when its output equals the voltage across the resistor 20. Conversely, when the output of exciter 27 is low, its bucking action willbe .lQWQQdaccordingly the excitation of fieldwin'ding-H or motor I9 Will be high.

Exciter 21 is provided with;a:se l;excited:fieldj;

winding 29 connected across its terminals in series with an adjustable resistor w w iohiwinding supplies the necessary ampere'turnsfor maintaining the field of the exciter at any poinkvzithin its regulating range. Exciter 21 is also provided with a reference field winding ,3! .,which at .one endis ,connectedtoone-side of: s,ou11ce, 1,5:and :at .its other end is connected ,to ,the ,opposite side of source IS in series with the resistanee ele- -,ment ofa rheostatgthi. .Rheostatfi preferably-mas its ad ustin el ment mechani a l coupled wit the, adjustingelementof rheostatili. gEXClQGI 21 .isiurthenpr vide withiasienal field-windingfi which is connected across aload resistorlzz ,in eseries withan. adjustable resistor-34. Exciter 21 may-be assumed torbe drivenat constant speed ;by 1a ;motor 3 5. Thepoi-nt common tothe highepo- ;tential terminal of exciter zl findzthElOlVRQtBlltial terminal of rectif erzj28 is. -connected through a. conductor;36 to; the point common betweenresisters-2,4: and 2 5.

The operation ofjthe system of -,Fig.-1 '.wi ll,now bedescribed.

,Let; it beiassumed that motor M is operating at some preset -spee d-=as determinedby the adjust- :ment of rheostats +5 and |8,-and that-the mate- :rial: IO'is'adVancing-tO Wind-up reel13 at 8.70013118- sponding constantlinear speed. It will-be observed that tachometer generator 23 will have ,some constant output voltage, 1and;that winding rheostatslzfi and. .32, the, curve thus a reduction in the C. E. M. E. of motor It to increase the current of the latter. However, when motor l9 reaches zero speed, its 0. E. M. F. will revert to zero, regardless of the action or" exciter '21, and current regulation by motor field control will, therefore, become ineffective. It is at this point that current regulation by generator volt- :age; control takeeeffect.

By virtueofjthe connection of exciter 2'! to winding 2i of generator 2|, as shown in Fig. 1, ,exciter 21 in increasing its output voltage to den reaseth e eitation 0f field 19a of motor creases its--proportionate excitation to winding ;-2 l of generator 2 Ito offset the reduction in the efiect-of thep. E M. F. of the motor. Thus, with motor i9:at:rrest,rexciter 21 efiectively regulates, through control of excitation of winding 2W of generator"2l,toinsure that motor I9 will exert listallcditorque on reel I3 and thereby maintain the desired value of tension on material It with ,reel teat rest. ..,It willbe. appreciated thatexciter 2;1-,will;r,egulate, in like manner toprovidesuch regulationin the ,-zero, speed regionwhen acceleri itlrig the mill ,motor l4 from ,rest to a preset 25 speed.

.li 2g aph ea lydepictshow in ti esystemw of Fi .1 exciter 1 acts to J int y re u ate th str n t -o fi ld H -o m t 1 vand th output .voltageofigenerator 2 i. For given settings of the .A represents the variation in flux: of motor [9 afiorded by, the action. of exciter 27, while the slanting line, B represents the variationin output voltage of genera- .tor,2 Lafiordedby exciter 21. The intersection of .the broken verticallineC with curveAandline ,as .a reeling.operationprogresses, under 21 m generator Zitvillhe subiectedto an-exci- .tation voltage which is proportional to. the output voltage of tachometer generator23. Asthediamteterotthe material :lU-on-reel i3 increases-the armature :of motor 7 t9 tends to draw increased current-and excitenzl functions in a well known :rnannertoincrease the strength of the fieldem Such; increase in: strengthof field l9 results in increase in the C. E. M. F.,-and hence a correction in the-,arinatur-e current oimotor l9. Asa result, 1

'rnotor i9 is permitted to slowgdown progressively wi h inc ease. in -,diam ter o t mate ial nn cr ek 3 tmma ntain c nstant; h rsepower :out u to reel l 3.

Now letitbe assnm dithatatthe end fza processi erep r i i m t r L iis:d leratedt restias :byradiu tment ofrrheestat l8 rte-decrease "the excitation pf zwinding I11 70f en rator :11 :to z o- ASL'IIIOEQI IALSIOWS d wn terrestfith -ou put-volt? ae ofi taehometeng n r teni 3 'w l iprogrcssivfi y decrease to zero, thus tending to decrease to, zero tl.'i e--,excitation of (winding? i of-generatonz The output voltage of; generator??? lxthus tends -:t,o.:; .sappear,.causingadecrease in the-reel motoncurrent and voltage drop v across resistor ;22. -The excitation ,of signaliield winding-3 3-; of exciter zl ct en byt ndste decre s and:theexciten-a or nel zm a esritse t trvolta e- :lznereasediout- Dut-Moltageqof exciter-gzl, results in:a;decrease::in theeexcitatiemo W ndin lifi zofmetor ta -and ,B may 1 be assumed .,to depict thepcndition of an -'empty ree1, :while the intersection of the broken everticalline D with curves A andB nay. beassumed to depictthe condition of av full reel. Thus st a y state conditionswithin' the limits of lines C and D, .theflux of motor l9 would increasein accordance .vviththe curveA, while the output voltage of gen- .eratoril rwoulddecreasein accordance with the .line .13: due to ,the regulating action of exciter 21. .If-ata conditionof afullreel, mill ,motor 14 is decelerated ,to rest, theniexciter'z'l will function to decrease the ,fiux of .motor [9 and increase the output voltage ofugenerator fl to therespective stabilized ivalues depicted by .theinterseetion of the brokenvertical line E with curve A and line B. Thesestabilized valuesofmotor fluxand generator output voltage obtain atstalled conditions. of ,motor- L9,; and -exciter ,2! regulates to .suchvalues henevertheoutput voltage ortachometer gengiven reel diameter exciterfz'i will bhllsre l late ,to;maintain-. a higher-value of currentin the loop circuit ofztheiar a u e of motor I 9 andv ge rator 2 l {Ihe;sa me holds true under-stalled conditi ns -meter wa de i ed e int rse tion Q t; 9 .l E ith eu ves..-A-= n,d.B. onrer elyse cite rfl ewi lr eiil tette main aimlowe values of running and stalled current by rnptor I9 when the adjusting element of rheostats 26 and 32 are repositioned in the clockwise direction from that shown in Fig. 1. Slanting line curve B" indicates how the output voltage of generator 2i would vary following a given repositioning of the adjusting element of rheostat 26 in the clockwis direction.

Referring to Fig. 3, it shows a modified form of control system aitording the same type of control as hereinbefore described. The control system depicted in Fig. 3 is in many respects similar to that shown in Fig. 1 and corresponding components bear the same reference numerals. The modified control system dispenses with the tachometer generator 23 and rheostat 25.

More particularly, field winding l'i of generator ii is connected at one end to one side of source and at its other end to an adjusting element of a potentiometer rheostat 4B, which has its resistance element connected across opposite sides of source 15. The adjusting element of rheostat it is mechanically coupled to the adjusting elements of rheostats M and 4i of a compound rheostat set 4|. The resistance element of rheostat M is connected across opposite sides of source i5 and its adjusting element is electrically connected to the midpoint on the resistance element of rheostat 4t The adjusting element of rheostat li is connected to one end of field winding fil of generator 2|, which field winding is connected at its opposite end to one side of source l5 in series with a resistor 32.

Rheostat set 4| is of the type disclosed in my copending application Serial No. 117,655, filed September 24, 1949, now Patent 2,634,386, having the resistance elements of rheostats ll and 41 complementally formed so that for any positioning of the adjusting elements the equivalent resistance of the rheostat set in the circuit aforedescribed will be constant. Reference should be made to the aforementioned copending application for a more complete understanding of the design and electrical characteristics of rheostat set 4 5.

Reference field winding 3| of exciter 21 is connected at one end to one side of supply source and at its other end to the adjusting element of a rheostat 43, which has its resistance element connected across source 15. The adjusting element of rheostat 43 is mechanically coupled to i the adjusting elements of rheostats 44 and 44 of a compound rheostat set 44, which is similar to the rheostat set M. The resistance element of rheostat 44 is connected across the armature terminals of exciter 21 and its adjusting element is electrically connected to the adjusting element of rheostat 44 Rheostat 44* has the midpoint of its resistance element electrically connected in series with a resistor 45 to a point common to the connection between field winding 2 l of generator 2i and the adjusting element of rheostat t i b of rheostat set 4 I.

It will be apparent that rheostat set M because of its mechanical connection with rheostat 4? will provide an energizing output voltage to winding 2 I of generator 2! in direct proportion to the voltage and speed of mill motor I4, and that the output voltage thereof will decrease to zero when motor Hi is decelerated to rest by deenergization of the field winding Il and a reduction to zero of the voltage of generator IT. For the adjustments of rheostat 43 and rheostat set 44 shown, the output voltage of generator 2! may be assumed to vary according to the curve B of Fig. 2 during a reeling operation and stabilize at the value depicted by the intersection of the vertical line E therewith under stalled conditions of motor 19. Shifting of the adjusting elements of rheostat 43 and rheostat set 44 in the counterclockwise direction will increase the output voltage of generator 2! at any reel diameter and at stalled conditions of motor is, such as for example in accordance with curve B of Fig. 2. Thus with such counterclockwise readjustment of the adjusting elements of rheostat 43 and rheostat set 4%, exciter 2! will act to provide increase in torque of motor l9, both during reeling and at stalled condition of motor l9. Conversely shifting of the adjusting elements of rheostat 43 and rheostat set 44 in the clockwise direction will efiect decrease in the output voltage of generator 2| at any reel diameter and at stalled condition of motor i9, such as, for example, in accordance with curve B" of Fig. 1. Thus, with such clockwise readjustment of the adjusting elements of rheostat 43 and rheostat set 44, exciter 21 will act to provide decrease in torque of motor i9, both during reeling and at stalled condition of motor is.

I claim:

1. In combination, an electric motor, a generator having its armature connected in a loop circuit with the armature of said motor, a constant excitation voltage source in circuit with the field winding of said motor, a second motor, means in circuit with a field winding of said generator for supplying the latter with an excitation volt age proportional to the speed of said second motor, and a regulator comprising an exciter having a control field winding connected to be responsive to the armature current of the first mentioned motor, said exciter having its armature connected to the field winding of said first mentioned motor in bucking relation to said source, and also having its armature connected in circuit with the aforementioned field winding of said gener ator to supply the latter with an excitation voltage proportional to the output voltage of said exciter.

2. In combination, an electric motor, a generator having its armature connected in a loop circuit with the armature of said motor, a constant excitation voltage source in circuit with the field winding of said motor, a second motor, a generator driven by said second motor and connected in circuit with a field winding of the first mentioned generator for supplying the latter with an excitation voltage proportional to the speed nected to be responsive to the armature current of the first mentioned motor, said exciter having its armature connected to the field winding of said first mentioned motor in bucking relation to the source, and also having its armature connected in circuit with the aforementioned field winding of said first mentioned generator for supplying the latter with an excitation voltage proportional to the output voltage of said exciter.

3; In combination, an electric motor, a generator having its armature connected in a loop circuit with the armature of said motor, a constant excitation voltage source in circuit with the field winding of said motor, a second motor, a generator drivin by said second motor, a pair of resistors connected in series circuit with the last mentioned generator and the field winding of the first mentioned generator for supplying the latter with an excitation voltage proportional to the speed of said second motor, and a regulator comraprisingzanexciter having ,ac-controlzfield winding zrconnectedz'to lbe responsive to: the :zarmature curi-rent :of the'ifirst': mentioned motor, :said exciter h-avingoits armature connected to: said field wind- -ing*of.said:first mentioneld motor.inbucking rela- {excitation voltage source in circuit with" the field -:windingroofzsaidsmotcr, :a second motor, a generiator driven i by said second :motor, first andzsec- .OIId'II'GSiStOIS connected in1series between one terminal 1 of the last mentioned generator and the ifield-windingzof {the first mentioned generator z'andiafiording supply of the-latter with anrexcitationvoltage proportional -to the'speed of said -:secnd:motor, a potentiometenrheostatyhavingrits resistance element connected across said-source and having its adjusting element connected to .the point common between said ,one terminal of .said last mentioned vgenerator I and said-firstg-re- -sistor, ,a second rheostat having its adjusting-element mechanicallywcoupled to :the zadjusting=.;ele- Fment ,cf said potentiometer ,rheostat, and ansexvciter, comprising a control field-windingcommcted .to be responsiveto-ithe armature current :of 'the .firstrmentioned motor, andcanother fieldawinding in circuit awitlrisa-idscurceandsaid -;second rheo- V-stat, said exciter having: its'armatureconnected to said field winding :of .said first mentioned :motorinibucking relationtocaid source, 1andzals0 ,ha-vingits armature connected-to the point commen-between osaid first and second :resistors'for supplying :said field 1 winding of :said first ---men- .tioned generator :with anxexcitation voltage pro- ,portionalto-the output voltageiof said-exciter.

.5. In combination; an electric motor, agenerator having its armature connected in a loopcir- .cuit with thegarinature oi-saidmotoiyarconstant excitation voltagesource in circuit with the-field winding of-said motor,,-a second motor, ;a::reg.u- :lator comprising-anv exciter having a. control'field winding connected to be responsiveto the tarma- .ture =current'of the first vmentioned :motor and ,havingits armature: connected to the, field wind- ,ing of'said first mentionedmotoriirbuckingn'elation to said-source, and tanetwork ,ainzcircuit with the field winding oisaid'generatoncomprish1g9, {first compound -rheostat .-set for :supplying the latter, field winding with an excitation :voltage proportional motile-speed :of-saidseccndamoator, :said network :f'urther :comprising a second compound :rheostat :set in circuit withthe armatureeofrsaid exciter and said'fieldwindingof said generatorifor .supplyingzthe latter with anexcita- -,tionvoltageproportional to the output :of said :exciter.

6. In combination,-:an;electric.motor,:a generatorchaving at-single ,field winding and having its armature connected in a loop circuit with the 1 field winding of i said first mentioned motor in t-of saidvmotona second motor, means in circuit withsaidfield'winding.oi said generator for sup- .plyingsithe latter with an 'excitationivoltage -proportionaltoithe speed :of: said second motor; and a regulator comprising an exciter having a control :field .winding connected 1 to 'be responsive to .the ,armature circuit of r the first mentioned smotor, saidexciter. having its" armature connected to the buckingv relation to 'said source, and. also 'having its armaturerconnected' in 1 circuit with i said :generator field'windmgzto. supply the latter .with an excitation voltage proportional tothecutputvolt- --age 20f said exciter.

7.. Incombination, an electric motor a generatort-having itsiarmature connected in a loopcirnected to ;be responsive .to thearmature current .ofithe first mentioned motor, said exciterhaving its armature connected :toithe 1field winding of the first mentioned motor vin'bucking relation to said constant excitation :voltage; source, and also -;having: itsarmature connected .in circuitxwiththe aforementioned field winding of said generator to supply the latter: with .anrexcitation .voltage:pro-

-portional to theoutputwoltagemf said exciter.

8. In combination, an element for working 'on *aastrip of materialda first electric motor for driving said element-a :reel :for said material; a second electric;-m0.tor f0rdriving said. ree1,:.a generator having itsarmatureconnected inaloop cir- 'cuit with the armaturecof :said: second motor, a constant excitation voltagesource in circuitwith the field winding of said second motor, meansin circuit withthe field winding of said generator for supplying the latter with .:-an excitation voltage proportional ,to the speed of .said first. motor; and a regulator comprising an-exciter having a controlfieldwinding connected to be responsive to the ,armature-current .of said second motor, said :exciter having itsarmatureconnected .tothe field winding of; said second motor in bucking relation .to said source, and also havingits armature con- :nected ;in circuit "with the aforementioned field winding ofsaid generator to supply the latter with an excitation voltage proportional to the i'cutputvoltagerof said exciter.

ERIC 'PELL.

ReferencesOited "in'the-file of this patent UNITED STATES PATENTS Number Name Date 12344248 Creverns "Junef29, 1948 24%,183 Kenyon, Nov. 16, 1948 "2,462,171 'Erbeetal. Feb.. 22, 19.49

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